The weighted mean of the area and a size-class distribution of the glomeruli were calculated with a computer-assisted planimeter in a series of autopsy kidney specimens of diabetic and non-diabetic Pima Indians. These morphometric variables were also related to the severity of histologic glomerular lesions, graded on a four class scale. Glomerular size did not differ in the two groups, nor were differences in the size distribution discernible among the classes of histologic lesions. A similar pattern was found in a Causcasian population with NIDDM. These data are in contrast to IDDM where there is an early increase in glomerular size, followed by a late decrease in glomerular size as end- stage renal disease supervenes. The glomeruli of diabetic Pima Indians did not decrease in size at the stage of diffuse sclerosis, a finding that contrasts with what is commonly seen in other types of kidney disease, especially those associated with vascular lesions. Comparisons between the size of the glomeruli in autopsy specimens from caucasian and black individuals devoid of renal disease was also undertaken.